(a) Technical Field
The present invention relates to a method and a device for controlling an electric power source such as a hybrid starter generator (HSG) of a hybrid electric vehicle (HEV), more particularly, it relates to a method and a device for controlling a change in torque of the electric power source connected to an internal combustion engine through a belt in the HEV by distinguishing situations in which tension influencing durability of a belt increases and does not increase in the HEV.
(b) Description of the Related Art
In general, a system connecting driving force by using a belt exists in a hybrid electric vehicle (HEV), and there are many cases in which an electric power source such as a hybrid starter generator (HSG) connected with an internal combustion engine is connected by the belt to serve to start the engine, output driving force, charge a battery, and the like.
The durability of the belt is influenced by a degree of tension required to pull the belt, and controlling a separate electric motor for preventing deterioration of durability is required.
In general, in a system in which the internal combustion engine and the electric power source are connected to each other by the belt, since rotational inertia of the intern combustion engine is still larger than that of the electric power source, control to prevent deterioration of the durability is performed by restricting a torque change rate of the electric power source.
However, when a uniform torque change rate is applied as described above, even at the time of performing control in which an absolute value of torque output from the electric power source decreases, a torque control speed of the electric power source decreases due to the restricted change rate, thereby influencing a control response. In a situation in which the torque absolute value of the electric power source actually decreases, the tension to pull the belt decreases, therefore, the belt durability is not influenced.
Accordingly, it would be desirable to restrict the change in torque of the electric power source by distinguishing the situations in which the tension influencing the durability of the belt increases and does not increase.
FIG. 1 (RELATED ART) is a configuration diagram illustrating a system connecting driving force by using a belt in a hybrid electric vehicle and illustrates a connection state of a hybrid starter generator (HSG) 70 which is an electric power source, a battery 60, an inverter 50, a driving motor 30, an engine clutch 20, a transmission 40, and a differential device 90 connected with an internal combustion engine 10 through a belt 80, and illustrates a system having a structure including an electrical path between the HSG 70 and the driving motor 30 and a mechanical path between the internal combustion engine 10, and the driving motor 30 and a wheel 100.
The transmission 40 may be constituted by an automatic transmission (AT) and multispeed transmissions including a double clutch transmission (DCT), and the like.
In such a system, a hydraulic control unit (HCU) performs control of the HSG 70 for controlling engine stop, a motor control unit (MCU) performs control of the HSG 70 and the driving motor 30, the transmission control unit (TCU) performs transmission control, and an engine management system (EMS) performs engine torque control.
The tension to influence the durability of the belt is a pulling force which is applied to the belt while the HSG 70 does not output the torque, and when the engine 10 outputs the torque, since inertia of the HSG 70 is relatively smaller than that of the engine 10, the durability of the belt is not significantly affected. However, when the HSG 70 outputs the torque to pull the engine 10, the durability of the belt needs to be considered due to a difference in inertia and a slew rate of the torque outputted by the HSG 70.
In a situation in which an absolute value of the torque of the HSG increases, the tension increases, which influences the durability of the belt depending on the tension; and in a situation in which the absolute value of the torque decreases, the tension is changed to decrease, which does not exert a large influence on the durability of the belt.
In other words, controlling a torque change rate of the HSG by distinguishing a situation in which the tension increases and a situation in which the tension decreases is required.
The slew rate as a gradient and a change rate of a line, which increase to a maximum value, may be regarded as a slope of the torque which is changed with time.
A line diagram illustrated in FIG. 2A represents a target torque of the electric power source (hybrid starter generator, or HSG) and a line diagram illustrated in FIG. 2B represents an actual torque of the HSG depending on the restriction of the slew rate.
As illustrated in FIG. 2, when a single slew rate is applied to the entire section of the torque control of the electric power source, a phenomenon in which a response is delayed in the entire torque area occurs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.